CN114574843A - Composite protective film, preparation method thereof and liquid lead bismuth corrosion resistant metal tungsten - Google Patents

Composite protective film, preparation method thereof and liquid lead bismuth corrosion resistant metal tungsten Download PDF

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CN114574843A
CN114574843A CN202210193235.1A CN202210193235A CN114574843A CN 114574843 A CN114574843 A CN 114574843A CN 202210193235 A CN202210193235 A CN 202210193235A CN 114574843 A CN114574843 A CN 114574843A
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protective film
liquid lead
bismuth
pbwo
composite protective
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马胜强
付沙沙
邢建东
吕萍
符寒光
郭鹏佳
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Xian Jiaotong University
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C22/02—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using non-aqueous solutions
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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Abstract

The invention discloses a composite protective film and a preparation method thereof, and liquid lead bismuth corrosion resistant metal tungsten, wherein a tungsten bar is cut into experimental samples; melting the lead-bismuth alloy to obtain liquid lead-bismuth; placing the treated experimental sample into a crucible containing liquid lead bismuth, fixing the sample, and carrying out interface reaction and diffusion reaction on W in the experimental sample and oxygen dissolved in the liquid lead bismuth to generate a layer of WO3A surface film; WO3The surface film further reacts with oxygen dissolved in the liquid lead bismuth and the liquid lead to regenerate a layer of PbWO4A protective film; finally, PbWO4Continuously reacts with oxygen dissolved in the liquid lead bismuth and the liquid lead to generate Pb2WO5. And taking out the experimental sample, placing the experimental sample on a stainless steel sheet, and cooling the experimental sample to obtain the metal tungsten with the protective film. The invention lays a foundation for expanding the application of refractory metals in industry.

Description

Composite protective film, preparation method thereof and liquid lead bismuth corrosion resistant metal tungsten
Technical Field
The invention belongs to the technical field of corrosion science and protection, and particularly relates to a composite protective film, a preparation method thereof and liquid lead bismuth corrosive resistant metal tungsten.
Background
Tungsten (tungsten), element symbol W, is silvery white and belongs to group vib in the periodic table. Tungsten has many physical properties that are unique among all metals, such as tungsten having a melting point as high as 3410 ℃, being the highest melting metal, its vapor pressure and evaporation rate being the lowest of all metals, and a linear expansion coefficient that changes with increasing temperature being the smallest among refractory metals. All these outstanding properties of tungsten open up a wide and important field of application for tungsten in various engineering, and tungsten and its alloys are widely used in the electronics, electric light source industries, and also in the aerospace, casting, weapons, etc. sectors for making rocket nozzles, die casting molds, armor piercing cores, contacts, heating elements, heat shields, etc. In addition, because tungsten has many advantages such as high melting point, low sputtering yield, high thermal stress coefficient, high density, large mass number, etc., it is a candidate material for fusion reactor structures and divertors, and spallation neutron source solid target applications, many of which need to be used in liquid metal coolant environments to minimize material and equipment damage caused by high heat flow and high energy proton beam irradiation.
However, liquid metal coolants cause serious corrosion problems to the above materials and equipment, forming so-called liquid metal corrosion damage. The liquid lead-bismuth (Pb-Bi) eutectic alloy has a plurality of advantages in the aspects of excellent chemical, physical, thermal hydraulic and neutronic performances and the like, so that the liquid lead-bismuth (Pb-Bi) eutectic alloy becomes an important advanced liquid metal coolant applied to the nuclear industry, and researches on corrosion protection and control measures of tungsten in the liquid lead-bismuth are rarely reported and need to be supplemented urgently.
At present, two protection modes are mainly adopted, firstly, an advanced alloy with high liquid metal corrosion resistance is developed by starting from metal, and secondly, a coating with liquid metal corrosion resistance is applied on the advanced alloy. Many studies have now shown that tungsten is less alloyed because the workability of the alloy becomes poor or completely non-plastic at room temperature when the amount of alloying elements added to improve corrosion resistance is increased, and therefore there are extremely limited measures and means to control the study of tungsten alloys against corrosion by liquid metals. The method for applying the coating often causes the problems of poor binding force between the coating and a substrate, high regulation and control difficulty of the coating, high cost and the like, so that the self-protection film for preventing further corrosion is generated by in-situ reaction between the material and a corrosion medium by virtue of the induction function of the environment, and the method is an ideal effective method for solving the corrosion problem of the material.
The research on the corrosion mechanism and protection of the refractory metal tungsten in the liquid lead bismuth is rarely reported.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a composite protective film, a preparation method thereof and liquid lead-bismuth corrosion resistant metal tungsten aiming at the defects in the prior art, provide an effective protection way for solving the problem that refractory metal tungsten is seriously corroded under liquid metal, and lay a theoretical foundation for the engineering application of refractory metal tungsten in structural materials in the nuclear industry.
The invention adopts the following technical scheme:
a process for preparing composite protecting film includes such steps as putting tungsten in liquid Pb-Bi alloy, interface reaction and diffusion reaction between tungsten and oxygen dissolved in liquid Pb-Bi alloy to form WO on the surface of tungsten3/PbWO4/Pb2WO5And (4) three layers of composite protective films.
Specifically, the melting temperature of the liquid lead-bismuth alloy is 200-220 ℃, and the heat preservation time is 60-90 min.
Specifically, the metal tungsten and the oxygen dissolved in the liquid lead-bismuth alloy are subjected to interface reaction and diffusion reaction to form WO3/PbWO4/Pb2WO5The three-layer composite protective film specifically comprises:
the temperature is controlled to be 550-600 ℃, and the oxygen concentration is 1.17-2 x 10-3wt.% for 20-40 h, firstly generating a layer of WO on the surface of the metal tungsten3A surface film; WO3The surface film further reacts with oxygen dissolved in the liquid lead-bismuth alloy and the liquid lead to generate a layer of PbWO4A protective film; PbWO4The protective film reacts with oxygen and liquid lead dissolved in the liquid lead-bismuth alloy againObtaining PbWO4/Pb2WO5A bilayer film.
Further, WO3The thickness of the surface film is 10 to 20 μm.
Further, PbWO4/Pb2WO5The thickness of the double-layer film is 10-20 μm.
Further, PbWO4/Pb2WO5The double-layer film is a dense columnar crystal protective layer with a micron-sized spinel structure.
Specifically, WO3/PbWO4/Pb2WO5The thickness of the three-layer composite protective film is 18-40 mu m.
The composite protective film is prepared according to the preparation method of the composite protective film.
Specifically, the melting point of the composite protective film is greater than 900 ℃.
The third technical scheme of the invention is that the composite protective film is arranged on the surface of the metal tungsten resistant to the liquid lead bismuth corrosion.
Compared with the prior art, the invention has at least the following beneficial effects:
the invention relates to a preparation method of a composite protective film, which comprises the following steps of putting a lead bismuth alloy into an alumina crucible to completely melt the lead bismuth alloy; vertically inserting metal tungsten into a crucible containing liquid lead bismuth, and fixing a sample by using a clamp so as to prevent the sample from inclining due to the buoyancy of the liquid lead bismuth; keeping the temperature in the furnace, taking out the pure tungsten sample with the protective film growing on the surface from the liquid lead bismuth by crucible tongs after the protective film is formed, and placing the pure tungsten sample on a preheated stainless steel sheet to slowly cool the sample. Through detection and characterization, comprehensive information such as specific components, morphology, thickness, density and the like of the protective film is obtained; micron-sized WO prepared by the method3/PbWO4/Pb2WO5The three layers of self-growing high-adhesion compact composite oxide films greatly improve the corrosion resistance of the refractory metal tungsten in the liquid metal, and simultaneously disclose the corrosion mechanism of the refractory metal tungsten in the liquid lead bismuth at high temperature.
Further, the melting point of the lead-bismuth eutectic alloy (Pb44.5 wt.% and Bi55.5 wt.%) is 123.5 ℃, and in order to ensure that the solid lead-bismuth is completely melted into liquid lead-bismuth, the melting temperature is controlled to be 200-220 ℃, and the heat preservation time is 60-90 min, so that the lead-bismuth alloy is completely melted.
Furthermore, the refractory metal tungsten has high mechanical property at high temperature, and is a good high-temperature structural material, but the application of the refractory metal tungsten can be realized only in a protective environment, such as hydrogen, vacuum, argon and the like. The problem of oxidation is a key issue that prevents the widespread use of tungsten and tungsten alloys at high temperatures. Because tungsten begins to oxidize at 300-400 ℃ in normal-pressure air and volatilizes at a temperature above 850 ℃, the oxidation tends to be severe along with the rise of the temperature. In order to ensure the sufficient formation of the protective film on the surface of the tungsten in the liquid lead bismuth, after the metal tungsten is put into the liquid lead bismuth alloy, the temperature of the liquid lead bismuth alloy is controlled to be 550-600 ℃, and the oxygen concentration is controlled to be 1.17-2 multiplied by 10-3wt.% and the time is 20-40 h.
Further, WO of the inner layer3The surface film is combined with the W interface of the substrate continuously, compactly, smoothly and smoothly, so that the protective film is tightly combined with the substrate and is not easy to fall off, and the protective film becomes a third barrier for preventing oxygen and liquid lead bismuth from corroding the niobium substrate.
Further, the inner layer WO3The thickness of the surface film is 10-20 mu m, the thickness of the protective film of the layer is in micron level, and the PbWO which well connects the tungsten substrate and the outer layer is played4/Pb2WO5The double-layer lead tungstate oxide film enables the oxide layer to be tightly combined with the substrate and becomes a third barrier layer for oxygen and liquid lead bismuth.
Further, outer layer of PbWO4/Pb2WO5The double-layer protective film is a micron-sized compact spinel-structured compact columnar crystal protective layer, and the double-layer protective film can be used for preventing oxygen from oxidizing the tungsten matrix at high temperature to a great extent. Meanwhile, the double-layer protective film also isolates the direct contact of the liquid lead bismuth and the tungsten matrix, and prevents the liquid lead bismuth from corroding the tungsten matrix.
Further, outer layer of PbWO4/Pb2WO5The thickness of the double-layer protective film is 10-20 μm, and after 20h of corrosion, the thickness of the double-layer protective film is about 10-15 μmAnd m, when the corrosion lasts for 40 hours, the thickness of the protective film is about 15-25 μm, and the double-layer protective film provides a double-layer barrier, so that the oxidation of oxygen to the matrix and the corrosion of liquid lead bismuth to the matrix are avoided to a great extent.
Further, a three-layer protective film for corrosion resistance of tungsten based on refractory metal under liquid metal with the thickness of 18-40 mu m is finally formed, and the three-layer protective film plays two protection roles on a W matrix: firstly, the protective film prevents further oxidation of oxygen to the W matrix in high-temperature liquid lead bismuth to a great extent, and improves the oxidation and corrosion resistance of refractory metal tungsten at high temperature; the direct contact between the liquid lead bismuth and the W matrix is isolated by the generation of the protective film, so that the dissolution and permeation corrosion of the liquid lead bismuth to the W matrix are prevented to a certain extent, and the dissolution and peeling of the W matrix are inhibited; the three-layer protective film has the characteristic of self-growing of a high-density and strong-adhesion three-layer composite protective film in a liquid lead bismuth environment, and the self-repairing and self-growing characteristics of the protective film in the service process are effectively realized.
In summary, the protective film prepared by the method of the invention has three layers of WO3/PbWO4/Pb2WO5The protective film has a film melting point of more than 900 ℃, can maintain good stability even at high temperature, and can be well combined with a matrix, so that the problems of falling off of the film and the matrix and the like are guaranteed to a great extent.
The technical solution of the present invention is further described in detail by the accompanying drawings and embodiments.
Drawings
FIG. 1 is a SEM image of a section of a sample taken at 20 h;
FIG. 2 is a cross-sectional SEM image of a sample taken at 30 h;
FIG. 3 is a cross-sectional SEM image of a sample taken at 40 h;
FIG. 4 is a macro topography of the W sample before and after etching according to the present invention;
fig. 5 is an SEM and EDS image of W immersed in a lead bismuth portion for 20 h.
Detailed Description
The technical solutions of the present invention will be described clearly and completely below, and it should be apparent that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In the present invention, all the embodiments and preferred methods mentioned herein can be combined with each other to form a new technical solution, if not specifically stated.
In the present invention, all the technical features mentioned herein and preferred features may be combined with each other to form a new technical solution, if not specifically stated.
In the present invention, the percentage (%) or parts means the weight percentage or parts by weight with respect to the composition, if not otherwise specified.
In the present invention, the components referred to or the preferred components thereof may be combined with each other to form a novel embodiment, if not specifically stated.
In the present invention, unless otherwise stated, the numerical range "a-b" represents a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range of "6 to 22" means that all real numbers between "6 to 22" have been listed herein, and "6 to 22" is only a shorthand representation of the combination of these numerical values.
The "ranges" disclosed herein may have one or more lower limits and one or more upper limits, respectively, in the form of lower limits and upper limits.
As used herein, the term "and/or" refers to any and all possible combinations of one or more of the associated listed items and includes such combinations.
In the present invention, unless otherwise specified, the individual reactions or operation steps may be performed sequentially or may be performed in sequence. Preferably, the reaction processes herein are carried out sequentially.
Unless otherwise defined, technical and scientific terms used herein have the same meaning as is familiar to those skilled in the art. In addition, any methods or materials similar or equivalent to those described herein can also be used in the present invention.
The invention provides a preparation method of a composite protective film for resisting liquid lead bismuth corrosion of metal tungsten, which comprises the steps of placing metal tungsten in static liquid lead bismuth at 550-600 ℃ for 20-40 hours, and generating three layers of WO with liquid metal high-temperature corrosion resistance on the surface of tungsten in situ3/PbWO4/Pb2WO5Protective film, three layers of WO3/PbWO4/Pb2WO5The protective film can prevent oxygen atoms dissolved in the liquid metal lead bismuth at high temperature from violently oxidizing the tungsten matrix and preventing the liquid lead bismuth from corroding the tungsten matrix to a great extent, and the corrosion resistance of the liquid metal tungsten at high temperature is improved. The protective film has a compact structure and is well combined with a matrix, so that an effective protection way is provided for solving the problem that the refractory metal tungsten is seriously corroded in liquid metal at high temperature; by detecting the components of the protective film, the structure, the characteristic thickness and the compactness of the film, data are provided for the corrosion behavior of the refractory metal tungsten in the liquid lead bismuth serving as the nuclear coolant, the corrosion mechanism of the refractory metal tungsten in the liquid lead bismuth at high temperature is disclosed, and the theoretical basis is laid for the engineering application of the refractory metal tungsten in the structural material in the nuclear industry.
The invention relates to a preparation method of a composite protective film, which comprises the following steps:
s1, cutting the tungsten rod into experimental samples;
cutting a tungsten rod wire into a plurality of experimental samples of 50x6x3 mm; and (3) grinding the experimental sample by a grinding machine, and ultrasonically cleaning by alcohol to remove sample linear cutting traces and oil stains.
S2, melting the lead bismuth alloy to obtain liquid lead bismuth;
wherein the lead bismuth alloy is high-purity lead bismuth alloy for the nuclear.
500g of lead-bismuth alloy for nuclei (Pb44.5%, Bi55.5%) was put into a 50ml alumina crucible, and put into a high-temperature energy-saving atmosphere furnace together; the melting temperature is 200-220 ℃, and the heat preservation time is 60-90 min, so that the lead-bismuth alloy is completely melted.
The lead bismuth alloy comprises the following steps: since the alumina crucible capacity is 50ml, 50ml of liquid lead bismuth is expected to be contained. The density of liquid lead bismuth at 600 ℃ was calculated according to the following formula:
ρLBE＝11096-1.3236T
wherein T is temperature in K; rhoLBEThe unit is kg/m3。
The mass of the required lead-bismuth alloy is calculated to be 500g according to the following formula:
MLBE＝ρLBE·VLBE
the real-time temperature of the liquid lead bismuth is accurately measured by the thermocouple, so that the failure of the protective film due to the difference of reaction temperatures is avoided.
Controlling the oxygen concentration to be 2 x 10-3wt.%, the calculation formula is as follows:
LogCo＝1.2-3400/T(673K＜T＜973K)
s3, placing the experimental sample processed in the step S1 into the liquid lead bismuth in the step S2 and fixing, wherein the W in the experimental sample and the oxygen dissolved in the liquid lead bismuth generate interface reaction and diffusion reaction, and a layer of WO is generated firstly3A surface film; WO3The surface film further reacts with oxygen dissolved in liquid lead bismuth and liquid lead to regenerate a layer of PbWO4A protective film; PbWO4The protective film reacts with oxygen dissolved in the liquid lead bismuth and the liquid lead again to generate a layer of Pb2WO5A protective film; finally form WO3/PbWO4/Pb2WO5And (4) three layers of composite protective films.
Putting the experimental sample into liquid lead bismuth, controlling the temperature to be 550-600 ℃, and controlling the oxygen concentration to be 1.17-2.04 x 10- 3wt.% and the time is 20-40 h.
Further, the thickness of the finally formed protective film for corrosion resistance of the liquid metal lower refractory metal tungsten is 18 to 40 μm.
The W in the experimental sample and the oxygen dissolved in the liquid lead bismuth are subjected to interface reaction and diffusion reaction, and a layer of WO with the thickness of 10-20 mu m is generated firstly3A surface film; WO3The surface film further reacts with oxygen and lead dissolved in the liquid lead bismuth to regenerate a layer of PbWO4Protective film, final upper PbWO4Continuously reacts with dissolved oxygen and lead to generate outermost Pb2WO5Outer layer of PbWO4/Pb2WO5The double-layer protective film is a dense columnar crystal protective layer with a micron-sized dense spinel structure; inner layer WO3The surface film and the tungsten interface of the matrix are combined continuously, completely and smoothly, and the PbWO is arranged on the outer layer4/Pb2WO5The thickness of the double-layer film is 10-20 mu m; outer layer of PbWO4/Pb2WO5The double-layer film is a dense columnar crystal protective layer with a micron-sized spinel structure.
And S4, taking out the experimental sample, and cooling to obtain the refractory metal tungsten with the self-protection film.
The film melting point of the protective film for corrosion resistance of metal tungsten at high temperature is more than 900 ℃.
Testing and characterization of the performance, material type, thickness, density, etc. of the protective film:
s501, observing the corrosion form of the protective film generation part immersed in the lead bismuth, and evaluating the capability of the protective film generated in the lead bismuth on improving the corrosion resistance of the refractory metal tungsten to the liquid lead bismuth at high temperature. The tungsten surface immersed in the lead bismuth creates a protective film with three layers and good bonding to the substrate. The three layers of protective films can not only prevent the oxidation of oxygen to the tungsten matrix at high temperature, but also prevent the corrosion of liquid lead and bismuth, thereby improving the corrosion resistance of the refractory metal tungsten at high temperature;
the material of the protective film is proved by the atomic ratio of W, O, Pb by using a field emission scanning electron microscope (model GeminiSEM 500), a matched energy spectrometer (EDS) and observing the specific morphology of the protective film and detecting and analyzing the components of the protective film.
S502, detecting specific substances of the corrosion sample surface protection film through XRD and EDS, and observing the appearance of the surface protection film by using SEM;
the 2 theta range of XRD is 10-90, the current is 200mA, the voltage is 40KV, and the scanning speed is 2 DEG/min.
S503, cold embedding the sample by using epoxy resin to prepare an interface sample, grinding by using sand paper, and polishing; by SEM and EPMA, the appearance of the interface protective film is represented, and the specific substance of the protective film is detected to obtain the comprehensive information of the protective film
And (3) carrying out cold inlaying on the sample by using epoxy resin, lightly grinding the prepared interface sample along the parallel direction of the interface by using 1000#, 1200# and 1500# SiC water sand paper in sequence, and polishing by using a diamond polishing agent and wool cloth so as to prevent the protective film of the interface from being damaged manually.
The protective film prepared by the method solves the problems of severe oxidation of the refractory metal tungsten at high temperature and corrosion of the liquid metal, improves the corrosion resistance of the refractory metal tungsten to the liquid metal at high temperature, and reveals the corrosion mechanism of the refractory metal tungsten in the liquid lead bismuth at high temperature.
The invention considers various defects caused by alloying, coating and the like, combines the advantages of chemical reaction, and generates three layers of protective films which can improve the corrosion resistance of the liquid metal at high temperature of the refractory metal tungsten in situ on the surface of the refractory metal tungsten for the first time by means of oxygen atoms dissolved in the liquid lead bismuth environment.
The protective film prepared by the invention is three layers of WO3/PbWO4/Pb2WO5The protective film has a melting point of more than 900 ℃, can maintain good stability even at high temperature, and can be well combined with the matrix, so that the problems of falling off of the film and the matrix and the like are guaranteed to a great extent.
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. The components of the embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
The experimental preparation process of the protective film generated in situ in the liquid lead bismuth by the refractory metal tungsten comprises the following steps:
the tungsten rods used in the test are provided by Yuqian metallic materials Co., Ltd, Hebei, China, and the impurity concentration detected by SEM-EDS is shown in Table 1, and the lead bismuth alloy used in the test is provided by Henan Huapu alloy materials Co., Ltd, China, and the impurity concentration detected by SEM-EDS is shown in Table 2.
Table 1 and table 2 show the impurity concentrations in the original refractory metals tungsten and lead bismuth alloys of the examples, respectively.
Table 1. impurity concentrations in W (wt.%)
Figure BDA0003525094650000091
TABLE 2 concentration of impurities (ppm) in original LBE
Figure BDA0003525094650000092
1) Cutting a tungsten bar into experimental samples of 50x6x3mm, lightly sanding with 1000#, 1200#, 1500# SiC waterproof abrasive paper, polishing with polishing cloth made of woolen cloth and 2.5 mu m diamond polishing agent, finally ultrasonically cleaning with alcohol for 20 minutes and drying, wherein the purpose is to remove pollutants adhered to the surface of the sample so as to avoid the problems of influence on the generation of a protective film, the structural density and the like;
2) cutting a large block of lead-bismuth alloy into small blocks by a cutting machine, weighing 500g of each part, ultrasonically cleaning for half an hour by alcohol and drying by blowing, wherein the aim is to remove pollutants attached to the surface of the lead-bismuth alloy, and the concentration of impurities in the lead-bismuth alloy is detected by a high-resolution scanning electron microscope and an energy spectrum and is shown in table 2. Putting each weighed lead-bismuth alloy into a 50ml high-purity alumina crucible, and putting the lead-bismuth alloy and the alumina crucible together into a high-temperature energy-saving atmosphere furnace; setting a program to enable the temperature in the furnace to rise to 200 ℃, and keeping the temperature for 60min to enable the lead-bismuth alloy to be completely melted;
3) vertically placing the sample into a crucible containing liquid lead bismuth, and fixing the sample by using a clampThe sample is held so as not to be inclined by the buoyancy of the liquid lead bismuth. The schematic diagram of the device is shown in fig. 2, and the length of the sample extending into the liquid lead bismuth is 25 mm. In order to ensure that oxygen is dissolved in the liquid lead bismuth, the oxygen concentration in the furnace is kept in a saturated state and the lead bismuth is taken out at the time of 20 hours. By sample preparation of the cross-section, obtaining a sample cross-section as shown in FIG. 1, it can be observed that three layers of WO are generated in situ3/PbWO4/Pb2WO5The thickness of the protective film was 20 μm.
Example 2
According to the scheme, the sample is taken out at 30h, the section of the sample of 30h is obtained by section sample preparation, the section of the sample is shown in figure 2, and three layers of WO generated in situ can be observed3/PbWO4/Pb2WO5The thickness of the protective film was 30 μm.
Example 3
According to the scheme, the sample is taken out at 40h, the section of the sample of 40h is obtained by section sample preparation, the section is shown in figure 3, and three layers of WO generated in situ can be observed3/PbWO4/Pb2WO5The thickness of the protective film was 40 μm.
Verification example 1
Testing and characterizing the material type, structure and the like of the surface protective film:
1) as shown in fig. 4, a macro-topography after etching can be observed.
2) And observing the part immersed in the lead and bismuth, wherein the part is divided into a lead and bismuth coating area and a lead and bismuth falling area, and the lead and bismuth falling area is the most direct contact and observation place of the surface of the protective film, so that the falling area is used as a main observation and detection object. FIG. 5 shows the surface morphology of a sample after W is immersed in liquid static lead bismuth at 600 ℃ for 20h at low magnification, the elements mainly distributed at the falling part of the lead bismuth are Pb, W and O can be observed through energy spectrum mapping, the atomic ratio of Pb, W and O is obtained by combining the area and scanning the average value through SEM-EDS points for multiple times, as shown in FIG. 5, Pb: W: O is approximately equal to 2:1:5, and the uppermost layer of the surface of the sample is preliminarily judged to be Pb2WO5. The appearance of the protective film at the lead-bismuth falling part is observed at high power, the protective films with different morphological structures can be found, and the surface is protectedThe film presents a micron-sized compact spinel structure, which indicates that the generated protective film is multilayer.
3) After the sample of 20h is treated and the lead and bismuth coated on the surface are removed, multiple times of XRD detection are carried out at the position closer to the matrix, and the result shows that WO exists3、PbWO4、Pb2WO5Three substances, from which are generated in sequence WO from the inside to the outside3、PbWO4、Pb2WO5The three-layer oxide film of (2).
Verification example 2
Testing and characterizing the structure, thickness, density and the like of the interface protection film:
and (3) cold embedding the sample by using epoxy resin, lightly grinding the embedded interface sample by using 1000# to 1500# fine water sand paper, and polishing the sample by using a diamond polishing agent and wool fabric to remove scratches so as to avoid influencing the observation of the interface. Ultrasonically cleaning a sample for 20min by using alcohol, drying, and finally characterizing and detecting by using a field emission scanning electron microscope and an energy spectrum, wherein the fruit production examples are as follows:
1) the protective film has a three-layer protective film structure at 40h, and has a three-layer barrier protection effect on a tungsten substrate: on one hand, the protective film blocks the permeation, enrichment and passage of oxygen to a great extent, so that the tungsten matrix is prevented from losing efficacy due to oxidation and the like; on the other hand, the protective film isolates the direct contact between the liquid lead bismuth and the tungsten, thereby preventing the corrosion, embrittlement and other adverse effects of the liquid lead bismuth on the tungsten;
2) the spot analysis was performed several times at different stratification positions closer to the substrate, and the results shown in tables 3-5 were obtained. According to the atomic proportions of elements of different layers, the innermost layer W: o ≈ 1: 3, the second outer layer Pb: W: O is approximately equal to 1:1:4, the outermost layer Pb: W: O is approximately equal to 2:1:5, and the sequential generation of WO from inside to outside is proved again3、PbWO4、Pb2WO5The three-layer composite oxide film.
Table 3 detection of atomic percent of elements in innermost layer of protective film
Figure BDA0003525094650000121
TABLE 4 atomic percent of elements in the next outer layer of protective film
Figure BDA0003525094650000122
Table 5 detection of atomic percent of elements in outermost layer of protective film
Figure BDA0003525094650000123
4) During the static corrosion of the refractory metal W at 600 ℃ in the liquid lead bismuth, WO is firstly generated3，WO3Further reacts with oxygen and lead to generate PbWO4Protective films, PbWO4Continuously reacts with oxygen and lead to generate Pb2WO5Finally, WO is formed3、PbWO4、Pb2WO5The three-layer oxide film has the following reaction equation:
W(s)+3O(dissolved)→WO3(s)
WO3(s)+Pb(l)+O(dissolved)→PbWO4(s)
PbWO4(s)+Pb(l)+O(dissolved)→Pb2WO5(s)
in summary, according to the preparation method of the composite protective film for resisting liquid lead bismuth corrosion of metal tungsten, disclosed by the invention, the micron-scale three-layer WO is generated on the surface of the W substrate in situ by virtue of a high-temperature environment of liquid lead bismuth through a chemical reaction for the first time3/PbWO4/Pb2WO5Three layers of protective films; the capability of the protective film for resisting liquid metal corrosion at high temperature of refractory metal tungsten is evaluated through experiments for the first time; the method avoids a plurality of defects brought by the traditional alloying and coating, provides an innovative solution for protecting the corrosion of the refractory metal tungsten in the liquid metal at high temperature, and discloses a corrosion mechanism of the refractory metal tungsten in the liquid lead bismuth at high temperature.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.

Claims (10)

1. A preparation method of a composite protective film is characterized in that metal tungsten is put into liquid lead-bismuth alloy, the metal tungsten and oxygen dissolved in the liquid lead-bismuth alloy generate interface reaction and diffusion reaction, and WO is formed on the surface of the metal tungsten3/PbWO4/Pb2WO5And (4) three layers of composite protective films.
2. The method for preparing the composite protective film according to claim 1, wherein the melting temperature of the liquid lead-bismuth alloy is 200-220 ℃, and the holding time is 60-90 min.
3. The method for preparing a composite protective film according to claim 1, wherein the metal tungsten and the oxygen dissolved in the liquid lead-bismuth alloy are subjected to an interfacial reaction and a diffusion reaction to form WO3/PbWO4/Pb2WO5The three-layer composite protective film specifically comprises:
the temperature is controlled to be 550-600 ℃, and the oxygen concentration is 1.17-2 x 10-3wt.% for 20-40 h, firstly generating a layer of WO on the surface of the metal tungsten3A surface film; WO3The surface film further reacts with oxygen dissolved in the liquid lead-bismuth alloy and the liquid lead to generate a layer of PbWO4A protective film; PbWO4The protective film reacts with oxygen and liquid lead dissolved in the liquid lead-bismuth alloy again to obtain PbWO4/Pb2WO5A bilayer film.
4. The method of manufacturing a composite protective film according to claim 3, wherein WO3The thickness of the surface film is 10 to 20 μm.
5. The method for preparing a composite protective film according to claim 3, wherein PbWO is used4/Pb2WO5The thickness of the double-layer film is 10-20 μm.
6. The method of manufacturing a composite protective film according to claim 3, wherein PbWO4/Pb2WO5The double-layer film is a dense columnar crystal protective layer with a micron-sized spinel structure.
7. The method for preparing a composite protective film according to claim 1, wherein WO3/PbWO4/Pb2WO5The thickness of the three-layer composite protective film is 18-40 mu m.
8. A composite protective film produced by the method for producing a composite protective film according to any one of claims 1 to 7.
9. The composite protective film for liquid lead bismuth corrosion resistance of metal tungsten according to claim 8, wherein the composite protective film has a film melting point of greater than 900 ℃.
10. A liquid lead bismuth corrosion resistant metal tungsten characterized in that the surface of the metal tungsten is provided with the composite protective film according to claim 8.
CN202210193235.1A 2022-02-28 2022-02-28 Composite protective film, preparation method thereof and liquid lead bismuth corrosion resistant metal tungsten Pending CN114574843A (en)

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